9,10-disubstituted anthracenes for use as photoconductors



3,548,059 9,10-DISUBSTITUTED ANTHRACENES FOR USE AS PHOTOCONDUCTORSEisuke Ishida, Moriguchi-shi, and Kazuhisa Morimoto,

Osaka-shi, Japan, assignors to Matsushita Electric Industrial Co., Ltd.,Osaka, Japan N Drawing. Filed Dec. 15, 1966, Ser. No. 601,875

Claims priority, application Japan, Dec. 16, 1965, 40/79,!)03,40/79,004; Dec. 29, 1965, 41/226; June 9, 1966, 41/37,603

Int. Cl. G03g 5/00 US. CI. 96-15 2 Claims ABSTRACT OF THE DISCLOSURE Thepresent invention is directed to novel electrophotographic materialshaving the formula wherein R represents a member selected from the groupconsisting of phenyl, naphthyl and benzanthryl and R represents a memberselected from the group consisting of hydrogen and CH R The inventionrelates to electrophotographic materials adapted for electrostaticprinting, and more particularly to photoconductive organic substanceswhich can be laminated on a conductive support layer.

Electrostatic processes for graphic reproduction and photography havebeen developed by many investigators for a long period of time, theirgoals being mainly limited to graphic reproduction on opaque papers.

After the best-known system called Xerography had been disclosed in theJournal of the Optical Society of America, vol. 38, No. 12, December1948, there appeared in the literature various modifications in thematerials and process. Conventional materials for the photoconductivelayer adherent to a conductive support layer include selenium, sulphur,zinc oxide and also organic substances such as anthracene,anthraquinone, poly-N-vinylcarbazole, polyacenaphthylene orpolyvinyltriphenylpyrazoline.

However, transparent photography by an electrostatic process has notbeen achieved successfully because transparent photographs are usuallyprojected in large magnification onto a screen and require highresolution, less fog and an exact reproduction covering half tone. It isimportant for obtaining excellent pictures on the screen that thephotoconductive layer is flexible, colorless and transparent as Well asphotoconductive.

Prior inorganic substances such as zinc oxide and selenium are notsufiiciently transparent. Organic substances mentioned above are notentirely satisfactory for transparent photography, because some of themhave an excellent photoconductivity, but a poor adhesion to theconductive layer and others have a high transparency and a highadherence but a poor photoconductivity. According to a conventionalmethod, a photoconductive organic substance is required to be admixedwith a resin binder which decreases the photoconductivity thereof forapplying to the conductive support.

It is an object of this invention to provide an electrophotographicmaterial which comprises a photoconductive and transparent organicsubstance.

A further object of this invention is to provide a photoconductive andtransparent organic substance which i United States Patent 0 ice can beapplied uniformly to a conductive support layer with or withoutemploying any organic colloid.

A further object of this invention is to provide a transparentelectrophotographic material which comprises a photoconductive andtransparent organic substance applied to a transparent conductivesupport layer.

Another object of this invention is to provide a method for making aphotoconductive organic substance which is characterized by a hightransparency adapted for preparation of a transparentelectrophotographic material.

These and other objects of this invention will become apparent uponconsideration of the following descriptl'on.

It has been discovered according to the invention that a photoconductivematerial adapted for an electrophotographic process can be prepared withthe aid of condensation compounds having a methylene linkage illustratedby the following general formula in which each of R and R is an aryl, orheterocyclic radical.

A condensation compound adapted for electrophotographic materialaccording to the invention can be prepared by the following chemicalreaction equation:

wherein A represents an aromatic compound or a heterocyclic compound andB represents an aromatic compound substituted by a halomethyl group or aheterocyclic compound substituted by a halomethyl group.

Various compounds A and B, as listed in Table I, are known.

TABLE I A-compounds Benzene Naphthalene Anthracene Acenaphthene1,2-benzanthracene N-ethylcarbazole 9-ethylanthracene9,10-dimethylanthracene 9,10-dimethoxyanthracene Carbazole AcridinePolystyrene Poly-l -vinylnaphthalene Poly-9-vinylanthracenePolyacenaphthylene Poly-N-vinylcarbazole Polyvinylcaridine B-compoundsBenzyl chloride Benzyl bromide 1-chloromethylnaphthalenel-bromomethylnaphthalene 2-chloromethylnaphthalene2-bromomethylnaphthalene 9, lO-dichloromethylanthracene9,10-dibromomethylanthracene 7-chloromethyl-1,2-benzanthracene2-chloromethyll-imidazole Z-chloromethyltetrahydrofuran 3-brornomethylquinoline Among these compounds there exist numerouscombinations of A and B. According to the invention it has beendiscovered that the combinations listed in Table II are operable forproducing the condensation compounds defined in the above generalformula.

TABLE II Reaction temper- Reaction Color of Formula Cataature timeresultant Number A-compound B-oompound lyst Solvent 0.) (hr.) product 1Benzene Benzyl chloride Zn Tetraehloroethano 60-70 6 White.

Anthraeene d d 70-80 4 Yellow. 3 1,2-benzanthracene "(10. 60-70 7 Do. 4-N-ethyloarbazole. 70-75 7 Do.

Anthracene 60-65 6 Pale yellow.

1,2-benzanthracene. 70-80 2.5 Do.

N-ethylcarbazole.. 60-70 2. White.

Benzene 60-70 5 Yellow.

Naphthalene. 70-80 5 Greenish yellow.

Anthraeene 60-65 1. 5 Brown. 1,2-benzanthracene 60-65 1. 5 Greenishyellow.

N-ethylcarbazole... 50-60 2 Pale yellow.

Benzene 60-70 1 White.

Naphthalene. 60-65 1 Green.

Anthracene. 60-65 1 Pale pink. 1,2-benzanthracene. 60-65 1 White.N-ethyloarbazole- 55-60 1. 5 Pale yellow. Polystyrene 60-70 4 Do.

19 Poly-l-vinylnaphthalene Dichloroethanm 60-70 4 Do.

Formula 8 The resultant condensation compounds corresponding to thecombinations of Table II are represented by the following chemicalformulae designated by the corresponding numbers of Table II:

Formula 1 Q Formula 2 Formula 3 Formula 4 Formula 5 3OII2-i Z Formula 6Formula 7 Formula 9 F0 rm ula 1 0 Formula 11 Formula 12 Formula 13Formula 14 Formula 17 Formula 19 CHz (I) H It is also requisite to ahigh production yield that the mixing ratio of A-compound and B-compoundbe controlled. The best ratio is 1.0 mole of A-compound and 0.7 to 3.0moles of B-compound.

A combination of A-compound and B-compound is dissolved in a solvent.Operable solvent for the combinations listed in Table II is ahalogenated hydrocarbon solvent, e.g. tetrachloroethane, dichloroethaneand/or chlorobenzene. A solution so produced is admixed with a catalystselected from the group consisting of zine powder, iron powder, tinpowder, cobalt powder, nickel powder and their combinations, and then isheated at a temperature of to 120 C. for 1 to 24 hours. Optimalcatalyst, heating temperature and time are described in Table II inconnection with the combination of A-compound and B-compound.

The aforesaid reaction for producing the novel photoconductive compoundsresembles the FriedelCraft catalyst reaction, but has many excellentmerits as follows in addition to producing superior photoconductivecompounds for electrophotography.

It is the first merit that the separation of catalyst from the reactionmixture is easy. In the Friedel-Craft catalyst reaction, the catalyst inthe resultant mixtures of reaction is required to be dissolved in anacid solution or an alkali solution for separation of resultant productand the resultant mixture must be washed out with Water. in the methodof the invention, the metallic powder catalyst can be filtered offeasily and be re-used. If a part of the aimed resultant product existsas a precipitate, it is suitable to filter the catalyst after dissolvingthe precipitate in an appropriate solvent which is added to theresultant mixture.

The second merit is that the said filtered-off catalyst retains itscatalytic activity for further uses.

The third merit is that the solvent used can be recovered bydistillation and be re-used.

The fourth merit is that the condensation compounds by the method inaccordance with the invention are free from any by-products and havesolubility in a solvent higher than that of the Friedel-Craft product.

As mentioned above, the condensation compounds in accordance with theinvention have superior properties as photoconductive materials incomparison with the condensation compounds produced by the Friedel-Craftreaction. Especially, a condensation compound according to Formula 12,i.e. a condensation compound of N-ethylcarbazole and9,10-dichloromethylanthracene, gives best results. The compound ofFormula 12 has high photoconductivity, high solubility and hightransparency, and it is easily applied to a transparent photoconductiveinsulating layer for electrophotography.

Following description will explain the preparation of novel condensationcompounds in connection with exemplary compounds. The details of thepreparation of other compounds of the invention will be clear to theskilled in the art upon consideration of preceding and followingdescriptions, since only analogy procedure will be required.

The reaction of benzene and benzyl chloride, corresponding to Formula 1is as follows: In a 100 ml. (milliliter) round-bottomed flask equippedwith a stirrer, a thermometer, a gas-inlet tube and a reflux condenser,are placed 2.4 g. (grams) of benzene, 2 g. of benzyl chloride, 50 ml. oftetrachloroethane and 1.2 g. of zinc powder. The mixture is stirred for6 hrs. at to C. under a slight stream of nitrogen and is cooled to roomtemperature (20 to 30 C.). The zinc powder is filtered off with suctionand then the filtrate is distilled to 7 ml. by a reduced pressuredistillation. The resultant solution is poured into 50 ml. of n-hexaneto yield a White precipitate which is filtered off and is dried to 1.2g. of a white powder free from halogen.

Formula 4: Analogously, a mixture of 3.8 g. of 1,2- benzanthracene, 1.89g. of benzylchloride, 50 ml. of tetrachloroethane and 1.0 g. of zincpowder is stirred for 7 hrs. at 70 C. under a slight stream of nitrogen.After the reaction is completed, the catalyst is filtered 01f and thefiltrate is distilled at a reduced pressure of 7 ml. The resultantsolution is added to 70 ml. of n-hexane. A pale yellow precipitate isobtained and is filtered off and is dried to 1.3 g. of pale yellowsubstance free from halogen.

Formula 7: Analogously, a mixture of 4.3 g. of N- ethylcarbazole, 3.5 g.of l-cliloromethylnaphthalene, 60 ml. of tetrachloroethane and 1.0 g. ofzinc powder is stirred for 2.5 hrs. at 60 C. under a slight stream ofnitrogen. After the filtration of the catalyst, tetrachloroethane isdistilled. According to the said procedure a white powder (2.9 g.) isobtained.

Formula 12: Analogously, a mixture of 18.8 g. of N- ethylcarbazole, 11g. of 9,10-dichloromethylanthracene, 1.5 g. of zinc powder and 240 ml.of tetrachloroethane is stirred for 2 hours. at 51 C. under a slightstream of nitrogen. After the filtration of the catalyst,tetrachloroethane is distilled. According to the said procedure a paleyellow powder (15.6 g.) is obtained.

The compounds to be used in accordance with the invention have very goodphotoconductivity and are particularly suitable for the preparation ofhomogeneous coatings of unlimited shelf-life.

If transparent supports are used, the electrophotographic images canalso be used as masters for the production of further copies of any sortof light-sensitive sheets and specially as reproduction in moviepictures. In this respect, the photoconductive compounds used accordingto the invention are superior to the prior substances such as seleniumand zinc oxide, because such materials do not form a solid solution witha binder material and exist in a suspension form which results in acloudy layer.

For the preparation of the photoconductive insulating layers it isadvantageous that said compounds according to the invention be asolution in organic solvent, e.g. chlorobenzene, methylene chloride,dichloroethane, tetrachloroethane, dioxane and their combinations. Thephotoconductive compounds according to the invention may be mixed withother organic photoconductive substances.

The photoconductive compounds according to the invention may be insuspension form for applying the supporting material.

When the novel photoconductive compounds are used in association withorganic colloid, the proportion of organic colloid to photoconductivecompound can be changed advantageously in a wide range. For example, amixture of 30 to 120 parts of resin and 100 parts of photoconductivecompound can be employed.

The novel compounds form satisfactory photoconductive insulating layerswithout any organic colloids. However, addition of suitable organiccolloid can improve the resultant photoconductive insulating layer.Operable organic colloids are as follows: natural and synthetic resins,e.g. phenol resins modified with rosin, coumarone resin, indene resins,polyvinyl acetal, polyvinyl butyral, polystyrene, polyvinyl acetate,polyvinyl cinnamate, polycarbonate, ketone resins and vinylchloridevinyl acetate copolymers. A mixture of the photoconductivecompound and one of the said operable organic colloids can produce ahomogeneous and transparent layer on a support, said layer beingconsidered to be a solid solution of said photoconductive compound andsaid organic colloid when dried.

The addition of plasticizer can be aimed at the further improvement inthe property of the photoconductive insulating layers.

Operable plasticizers are as follows: chlorinated diphenyl, dimethylphthalate, diethyl phthalate and dioctyl phthalate.

It has further been known that the spectral sensitivity of thephotoconductive layer can be extended into the visible part of thespectrum by adding dyestufi? sensitizers or chemical sensitizers.

Excellent sensitizing effects can be produced by addition of 0.02 to 0.5weight part of the said dyestuffs to 100 weight parts of photoconductivecompound.

Particularly preferable as dyestutf sensitizers are triarylmethanedyestuffs such as brillian green, victoria blue B, methyl violet,crystal violet; xanthene dyestuffs, such as rhodamine B, rhodamine 6G,rhodamine G extra; thi- 8 azine dyestuffs such as methylene blue andtheir combinatlons.

Particularly preferable as chemical sensitizers are picric acid,tetrachlorophthalic anhydride, naphthalic anhydride,3,6-dinitronaphthalic anhydride, Z-methylanthraquinone,1,2-benzanthraquinone. Preferable amounts thereof are from 0.2 to 20weight parts with respect to 100 weight parts of the saidphotoconductive compounds.

The operable materials for electroconductive supports may be made of anymaterials which satisfy the requirement of electrophotography, e.g.metal plate or glass plate having NESA coating plates or foils made ofelectrically conductive resins or coated with evaporated thin metallayer, or paper. The solutions of the compounds of the photoconductivematerials, with or without the resins, are applied to the supports inthe usual manner, for example by spraying, by direct application, bymeans of rollers, etc., and then dried so as to produce a homogeneousphotoconductive layer on the electroconductive support. The transparentsupport can produce a transparent electrophotographic plate or foil.After an electrostatic charge has been applied, i.e. after the layer hasbeen charged positively or negatively by means of a corona discharge,the layer becomes light sensitive.

The reproduction of images by electrophotographic methods is carried outas follows; when the photoconductive layer has been charged, by means ofcorona discharge with a charging apparatus maintained at 6000-7000volts, the support with the sensitized layer is exposed to light under amaster and is then dusted over in known manner with a resin powdercolored with carbon black. The image that now becomes visible can easilybe wiped off. It can also be fixed by heating at about 120 C. Frompositive masters, positive images characterized by good contrast areproduced.

The invention will be further illustrated by reference to the followingspecific examples:

(1) 1 g. of the compound of Formula 1, and 0.5 g. of polyvinylcinnamateand 0.1 g. of Z-methylanthraquinone are dissolved in 7 ml. ofmonochlorobenzene. The solution is applied to an aluminum plate by meansof whirler coating and is dried to form a layer of 4 in thickness. Afterthe said aluminum plate provided with the layer is charged positively bymeans of corona discharge with a charging device maintained atapproximately 6000 volts in the dark, it is placed under a positivemaster and is exposed for 20 seconds to a 100 w. tungsten lamp at anillumination of 1000 luxes, and the said plate is powdered over with adeveloper in a per se known manner. This developer consists of toner andcarrier. The toner is composed of a low melting-point polystyrene,colophony and carbon-black. The toner is mixed with a carrier substancehaving such nature that the toner becomes triboelectrically charged witha charge that is the opposite of that produced on the plate, e.g. glassballs or iron filings. A positive image is produced which is fixed byslight heating.

(2) 1 g. of the compound of Formula 3, 0.5 g. of polycarbonate resin and1 mg. of crystal violet are dissolved in 7 ml. of methylene chloride.The solution is applied to an aluminum plate and is dried. Anelectrophotographic image is produced in a similar way to that describedin Example 1. It is exposed for 2 second to light of 250 luxes.

(3) 1 g. of the compound of Formula 5, and 0.5 g. of vinylchloride-vinyl acetate copolymer are dissolved in 7 ml. ofmonochlorobenzene. The solution is applied to an aluminum plate and isdried to form a layer of 4 in thickness. An electrophotographic image isproduced in a similar way to that described in Example 1. It is exposedfor 10 second to light of 400 luxes.

(4) 1 g. of the compound of Formula 5, 0.5 g. of polyvinyl acetate, 0.1g. of tetrachlorophthalic anhydride and 1 mg. (milligram) of methyleneblue are dissolved in 7 ml. of methylene chloride. The solution isapplied to an aluminum plate and dried to form a layer of 4 inthickness. An electrophotographic image is produced in a similar way tothat described in Example 1. It is exposed for 6 seconds to light of 250luxes.

(5) 3 g. of the compound of Formula 7, and 1.5 g. of polystyrene aredissolved in 9 ml. of monochlorobenzene. The solution is applied to acellulose diacetate film sheet which surface is in advancevacuum-evaporated with cuprous iodide by means of a blade coating and isdried to form a layer of 8p. in thickness. On this transparent sheet anelectrophotographic image is produced in a similar way to that describedin Example 1. It is exposed for 25 seconds to light of 1000 luxes. Itcan then be used as intermediate originals for further duplication, e.g.for copying on diazo paper.

(6) 3 g. of the compound of Formula 7, 1.5 g. of polystyrene and 3 mg.of crystal violet are dissolved in a mixture of 2 ml. of methylenechloride and 7 ml. of monochlorobenzene. The solution is applied to atransparent support and is dried to form a layer of 8 in thickness. Anelectrophotographic image is produced in a similar way to that describedin Example 1. It is exposed for 4 seconds to light of 200 luxes.

(7) l g. of the compound of Formula 8, and 0.5 g. of polystyrene aredissolved in ml. of tetrachloroethane. The solution is applied to analuminum plate and is dried to form a layer of 4 in thickness. Anelectrophotographic image is produced in a similar Way to that descriebdin Example 1. It is exposed for 2 seconds to light of 60 luxes.

(8) 1 g. of the compound of Formula 9, and 0.5 g. of polyvinyl butyralresin are dissolved in 10 ml. of monochlorobenzene. The solution isapplied to an aluminum foil and is dried to form a layer of 4a inthickness. An electrophotographic image is produced in a similar way tothat described in Example 1. It is exposed for 4 seconds to light of 500luxes.

(9) 3 g. of the compound of Formula 12, and 1.5 g. of vinylchloride-vinyl acetate copolymer are dissolved in a mixture of 8 ml. oftoluene and 2 ml. of methyl ethyl ketone. The solution is applied to anelectroconductive plastic film of a surface conductivity of 10 t'l-cm.and is dried to form a layer of 8a in thickness. After the film ischarged negatively by means of corona discharge in the dark, the saidfilm is placed under a positive master and is exposed for seconds to atungsten lamp at an illumination of 500 luxes, and the said film ispowdered over With a developer in known manner. A positive image isproduced which is fixed by slight heating.

(10) 3 g. of the compound of Formula 12, 1.2 g. of

polycarbonate resin and 0.2 g. of 3,6-dinitronanphthalic anhydride aredissolved in a mixture of 3 ml. of dichloroethane and 12 ml. ofmonochlorobenzene. The solution is applied to a transparent support asdescribed in Example 5 and is dried to form a layer of 10 in thickness.An electrophotographic image is produced in a similar way to thatdescribed in Example 1 on the said transparent support. It is exposedfor 2 seconds to light of 50 luxes.

(ll) 3 g. of the compound of Formula 12, 1.5 g. of polyvinylcinnamateand 3 mg. of crystal violet are dis solved in 12 ml. ofmonochlorobenzene. The solution is applied to a transparent support asdescribed in Example 5 and is dried to form a layer of 10 in thickness.An electrophotographic image is produced in a similar way to thatdescribed in Example 1. It is exposed for 2 seconds to light of 50luxes.

(l2) 3 g. of the compound of Formula 13, 1.5 g. of polyvinylcinnamateand 0.15 g. of 1,2-benzanthraquinone are dissolved in 12 ml. ofmonochlorobenzene. The solution is applied to a transparent plastic filmhaving an electroconducting layer of 10 SZ-cm. and is dried to form alayer of 10a in thickness. The said film is provided with a negativecharge by the corona discharge. After the film has been exposed for 2seconds to light of 50 luxes under a master, the image produced thereonis developed by powdering over with a developer, in a similar way tothat described in Example 1. The resultant positive image of mastershows excellent contrast likewise.

(l3) 1 g. of the compound of Formula 14, 0.5 g. of polystyrene and 10mg. of naphthalic anhydride are dissolved in 7 ml. of monochlorobenzene.The solution is applied to an aluminum plate and is dried to form alayer of 4 in thickness. An electrophotographic image is produced in asimilar way to that described in Example 1. It is exposed for 2 secondsto light of luxes.

(14) 1 g. of the compound of Formula 16 and 0.5 g. of polystyrene aredissolved in 7 ml. of monochlorobenzene. The solution is applied to analuminum plate and is dried to form a layer of 4 in thickness. Anelectrophotographic image is produced in a similar way to that describedin Example 1. It is exposed for 4 seconds to light of 100 luxes.

(15) 1 g. of the compound of Formula 16, 0.5 g. of polystyrene and 10mg. of picric acid are dissolved in 7 m1. of monochlorobenzene. Thesolution is applied to an aluminum plate and is dried to form a layer of4,u in thickness. The said plate is provided with a negative charge bythe corona discharge. After the plate has been exposed for 2 seconds atlight of 100 luxes under a master, the image produced thereon isdeveloped by powdering over a developer, in a similar way to thatdescribed in Example 1. The resultant positive image of master, showsexcellent contrast likewise.

(l6) 1 g. of the compound of Formula 18, 0.1 g. of2-methylanthraquinone, 0.5 mg. of Rhodamine G and chlorinated diphenylare dissolved in 15 ml. of tetrahydrofuran. The solution is applied toan aluminum plate and dried to form a layer of 4 1 in thickness. Anelectrophotographic image is produced in a similar way to that describedin Example 1. It is exposed for 2 seconds to light of 100 luxes.

What is claimed is:

1. An electrophotographic material comprising a conductive support layerand a photoconductive insulating layer, the latter comprising compoundshaving the for- References Cited UNITED STATES PATENTS 9/1966 Noe et al.96l.5 11/1966 Hoegl 96-1.5

GEORGE F. LESMES, Primary Examiner M. B. WITTENBERG, Assistant ExaminerUS. Cl. X.R.

